Integrated circuit chip manufacturers fabricate semiconductor devices layer by layer on semiconductor wafers. The layers may comprise various dielectric layers or insulating layers in addition to one or more of the following conductive layers: a thin metal coating such as tungsten or aluminum, copper, or gold, a thin polysilicon coating doped with conductive impurities, and other layers of metal silicides and metal nitrides. Normal chip manufacturing includes formation of various patterned layers of different materials in sequence on a semiconductor substrate such as silicon. The semiconductor wafer accepts the conductive metal coating, or polysilicon coating, or metal oxide coating as thin film or films usually less than 1 .mu.m thick. Process control and manufacturing tolerances apply to these sequential fabrication processes. Usually deviations from specified target tolerances in excess of only a few percentage points may result in defective and rejected semiconductor chips. Semiconductor device manufacturers usually can only discard defective semiconductor chips, thus resulting in undesirable production process waste and increased device manufacturing costs. A need thus exists for accurate techniques to measure physical parameters of various material layers including conductive layers during the fabrication process. These physical properties include the conductive layer thickness, sheet resistance, and substrate temperature during a fabrication process step.
Methods for applying semiconductor wafer conductive layers include processes known as chemical-vapor deposition (CVD), evaporation, and physical-vapor deposition (PVD) or sputtering. These thin film deposition processes usually take place in vacuum tight deposition chambers, such as these called Automated Vacuum Processors (AVPs) filled with process gases containing the chemical species for deposition of metals such as tungsten or aluminum. In single-wafer deposition equipment, the semiconductor wafer normally rests face downward or upward on support pins in the deposition chamber. During the CVD process, a lamp or some other heat source raises the wafer temperature to cause the wafer to interact with the process vapors. That process results in deposition of the desired conductive layer on the semiconductor wafer.
It is important to know conductive layer physical properties in real-time and in situ during PVD and CVD processes as well as during etch processes employed to form the necessary layer patterns. Also, monitoring various process parameters can provide important information regarding the deposition process itself and can be used for real-time process control applications. Both CVD and PVD processes, however, require noninvasive real-time, in situ conductive layer thickness or sheet resistance measurements for effective and reliable process control and process end-point detection. However, known methods of direct conductive layer physical property measurement usually require some sort of physical contact with the conductive layer on the wafer. But, physical contact with the wafer in the processing equipment disrupts the deposition process and may reduce the device manufacturing yield.
Known methods of process control during fabrication of conductive layers usually entails monitoring and control of process parameters such as wafer temperature, deposition or etch process duration, and process gas flows and pressure. These control methods are based on statistical process control techniques and use statistical process data to adjust process parameters during the deposition or etch process. These process control techniques, however, can often provide only indirect indication of actual conductive layer physical properties during and at the end of the deposition or etch process based on some previously measured deposition or etch kinetics data.
Conventional testing methods are used for direct semiconductor conductive layer measurements only outside the processing reactor and after the conductive layer deposition process ends. Thus, at that point the manufacturer removes the semiconductor wafer from the fabrication chamber to directly measure whether the conductive layer meets the necessary physical specifications for its design application. This method for determining semiconductor wafer conductive layer physical characteristics is, therefore, both non-real-time, and ex situ. This measurement method thus has little real-time process control value to the manufacturer and has use only in post-process quality assurance and statistical process control.
Consequently, a need exists for a method and apparatus for making real-time, in situ, non-invasive semiconductor wafer conductive layer physical property measurements. A need also exists for a technique to provide more complete information on plasma physical properties during the plasma deposition or etch process. These plasma physical properties include plasma density.